Treatment of subterranean formations containing water-soluble minerals



United States Patent i Patented July l2, 1960* TREATMENT OF SUBTERRANEAN FoRMA'rIoNs] CONTAINING WATER-SOLUBLE MINERALS Alden W. Hanson, Midland, Mich., assignor to The Dow from the subterranean formation Chemical Company, Midland, Mich.,"a corporation of Delaware No Drawing. Filed Feb. 24, 19s9,ser.No;794,s4s;-=

5 Claims. (Cl. 262-3) The invention is related to solubilizing water-soluble minerals in a subterranean formation and to removing rangement of concentric pipes inserted into a well'pene; trating the mineral stratum, the inner pipe usually-being the input line and the outer pipe being the output line. Another and more effective method is that described in US. Patent No. 2,850,270 which employs two or more separate wells, which penetrate the same soluble mineralbearing stratum, of which at least one well is an input well and at least, one other well is an output well. Communication is provided between said input and output Wells by hydraulically fracturing theformation,*'i.e.;by injecting a fluid into one of the Wells at sufiicient pressure to .produce cracks or fissures in the formation, at least some of such fissures intercepting both an input and output well. Fluid is then circulated down theinput well, along a fissure to the output well, and out the output well. Such circulation which is of small and relatively ineffectual volume at first is thereby gradually increased in accordance with that invention by forming a channel between the inputand output wells along the crack or fissure thus produced. The inherent difliculty existing in forming such a channel, due to the dissolution by the solvent of the mineral adjacent tothe input well until the point of saturation is reached at which dissolution stops, is overcome according to that invention by inhibiting the dissolving action of the solvent until it has progressed to more remote extremities of the fissure. A number of ways of effectively accomplishing the channeling are described in said U.S. Patent No. 2,850,270.

A particularly effective method of channeling through a formation, e.g., a salt stratum or bed between wells therein described in that patent is the embodiment designated (4) beginning-at line 69 of column 3 and com; pleting at line 2, column 4. The embodiment there described consists essentially of pumping a slurry of crushed or chipped ice in water down an input well, i.e., one of two or more wells intercepted by a fissure in a formation, at a pressure sufiicient'to force the slurry through the fissure and up an output well, i.e., another well intercepted by the fissure. The slurry of ice and water attains the objective of the invention, viz. channeling between wells, because the ice gradually melts to water, thus providing additional solvent as the slurry progresses away from the input well. It is recommended that the slurry when pumped down the input Well contain as much crushed ice as will permit the slurry to be readily pumped the minerals so solu-' erally, in water at higher temperatures.

so that someice will remain throughout the course to .theoutputwelh However, shouldall the ice be removedfrom at least portions of the water of-the slurry before reaching the output well, some additionaldissolution will occur as the result ,of increased solubility of A disadvantage associatedwith 'channelin-g through a water-soluble mineral in accordance'wi'th the embodiment of US. Patent 2,850,270 is that the heat of the formation requires large volumes of the ice and water slurry to be employed before the area of the formation exposed the appended 'claims.

along .fissures in contact with the slurry, have been sufficiently cooled to permit appreciable amounts, of the ice to remain unmelted for considerable distances from the input well.

A need, therefore, exists for a more expedient, economical, and effective method of channeling between wells penetrating a soluble mineral stratum.

The invention meets this need, by the employment of the steps hereinafter described and concisely defined in It consists essentially of animprovement of U.S. Patent 2,850,270 wherein a cold, aqueous solution is circulated through the fissures, pores,

and cavities in or adjacent'to a solubilizable miner-al- .stratum or bed' prior to circulating a slurry of .ice in:

1 water therethrough, said solution being nearly or fully may be ground, chipped, crushed, or broken into pieces saturated and preferably of the mineral inthe stratum to be subsequently solubilized hereinafter referred to as brine. The temperature of the brine must be substantially'below that of the formation and preferably near the freezing temperature of the solution At'least two wells must penetrate theformation'and communication exist therebetween. t

' In practicing the invention, at least tured according to a known fracturing procedure, e.g., that described in Reissue Patent 23,733 to Farris. To

proceed to the next step, at least one other well must.

exist in the formation or be drilled at this time'which intercepts at least one fissure produced in the fracturing operation. It'is unimportant whether the other well or wellsexisted before fracturing or after fracturing ofthe first well. Two or more of the wells may be fractured if desired. The practice usually. followed is to drill two wells at a distance of between a few hundred feet and a few hundredyards apart, both wells penetrating the stratum of water-soluble mineral. One of the wells is fractured to effect communication between the wells.

A brine, usually near saturation of the mineral of the type in the stratum, is prepared and cooled by well known refrigeration means, for example, by employing a unit whereby the brine to be cooled is circulated incontact with pipes carrying a circulating gas which has been brought down to a temperature well'below 0 C. by its rapid expansion just prior to or during the period of contact with the brine.

The cold brine is pumped down one well, forced through a fissure into a second well and forced therefrom back to the refrigeration unit thereby providing a continuous circulation of the cooling brine. Any well known pumping arrangement may be employed, eg those employed in deep well pumping units.

After the exposed faces of the formation walls are cooled, preferably to a temperature not substantially above 0 C., a slurry of ice and water is injected down one of the wells into the stratum in communication with another well. Usually the same input and output wells employed in the cooling circulation'are employed for the ice and water slurry circulation. The ice employed or bits of any convenient sizes and will be referred to salts, genone well'mustiexist or be drilled into a formation comprising a stratum oii"v water-solubilizable,mineral. The'formatio n is then frachereinafter as fragments. The-effectiveness of the ice slurry, as preceded by the brine cooling procedure of the invention, is now highly effective for channeling along a connecting fissure between the input and an output we'lL- As the ice slurry progresses along the fissure, or fissures, away from the input well, the ice continues to melt thereby releasing additional solvent at increasing distances from the input Well. The abrasive action of the ice'aids to some extent the enlargement of fissures along the course leading to the output well.

The potentialities of the use of the aqueous slurry of ice fragments employed in US. Patent 2,850,270 are fully realized by the practice of the instant invention. By circulating a cooling brine through the water-soluble formation prior to "injecting the ice water slurry effects substantial savings in the amount of ice consumed, renders the ice slurry injection much more effective by decreasing the time required to create adequate channels through the soluble stratum between wells and making channels of larger diameter entirely through the stratum up to the output well.

Having described the invention, what is claimed and desired to be protected by Letters Patent is:

1. The method of treating a subterranean formation having a temperature above C. containing a stratum of a water-solubilizable mineral traversed by a plurality of wells, at least two of said wells being in communica tion with each other through at least one fissure in the stratum which intercepts both wells, consisting of injecting down at least oneof the wells in communication, along the intercepting fissure therebetween, and out at least one other of said wells in communication, at a tempera ture below 0 C, a flow of cold brine followed by a two of said wells, circulating down one of said wells, designated input well, and out another of said wells, designated output well, a cold brine at a temperature below 0 C., continuously injecting down the input well an aqueous slurry of ice fragments, said ice gradually melting as the slurry progresses through said stratum, and continuously pumping the water of said aqueous slurry containing said mineral dissolved therein from the out-- put well.

3. The method of claim 2, wherein only one weil is sunk in said formation prior to fracturing' the formation and the other of said wells intercepting a fracture in the formation is sunk subsequent to fracturing.

4. The method of mining a salt from a natural salt bed having a temperature above 0 C. consisting essentially of drilling a plurality of holes into the salt bed, one of said holes being an input hole and one an output hole, fracturing said bed to producefractures therein, at least one of said fractures intercepting both input and output holes to provide-communication therebetween, circulating a highly concentrated brine at a temperature not above 0 C. into said input hole, thence through the V communicating fracture thus produced and out said output hole, pumping an aqueous slurry of ice fragments -ering the salt from the water of the ice slurry being flow of an aqueous slurry of ice fragments to enlarge and extend passageways between said Wells.

2. The method of treating a subterranean formation having a temperature above 0 C. having a water-solubilizable mineral stratum therein consisting of drilling at least two wells into said stratum, fracturing said stratum to produce a fracture in the stratum extending between pumped from said output hole, and circulating water through the channel thus formed to dissolve additionalsalt and carry it in solution out of the output hole and recovering the additional salt thus dissolved.

References Cited in the file of this patent UNITED STATES PATENTS 2,850,270 Hanson Sept. 2, 1958 

1. THE METHOD OF TREATING A SUBTERRANEAN FORMATION HAVING A TEMPERATURE ABOVE 0*C. CONTAINING A STRATUM OF A WATER-SOLUBILIZABLE MINERAL TRAVERSED BY A PLURALITY OF WELLS, AT LEAST TWO OF SAID WELLS BEING IN COMMUNICATION WITH EACH OTHER THROUGH AT LEAST ONE FISSURE IN THE STRATUM WHICH INTERCEPTS BOTH WELLS CONSISTING OF INJECTING DOWN AT LEAST ONE OF THE WELLS IN COMMUNICATION, ALONG THE INTERCEPTING FISSURE THEREBETWEEN, AND OUT AT LEAST ONE OTHER OF SAID WELLS IN COMMUNICATION, AT A TEMPERATURE BELOW 0*C., A FLOW OF COLD BRINE FOLLOWED BY A FLOW OF AN AQUEOUS SLURRY OF ICE FRAGMENTS TO ENLARGE AND EXTEND PASSAGEWAYS BETWEEN SAID WELLS. 